title: Atomistic simulations of uranium incorporation into iron (hydr)oxides.
abstract: Atomistic simulations were carried out to characterize the coordination environments of U incorporated in three Fe-(hydr)oxide minerals: goethite, magnetite, and hematite. The simulations provided information on U-O and U-Fe distances, coordination numbers, and lattice distortion for U incorporated in different sites (e.g., unoccupied versus occupied sites, octahedral versus tetrahedral) as a function of the oxidation state of U and charge compensation mechanisms (i.e., deprotonation, vacancy formation, or reduction of Fe(III) to Fe(II)). For goethite, deprotonation of first shell hydroxyls enables substitution of U for Fe(III) with a minimal amount of lattice distortion, whereas substitution in unoccupied octahedral sites induced appreciable distortion to 7-fold coordination regardless of U oxidation states and charge compensation mechanisms. Importantly, U-Fe distances of ∼3.6 Å were associated with structural incorporation of U and cannot be considered diagnostic of simple adsorption to goethite surfaces. For magnetite, the octahedral site accommodates U(V) or U(VI) with little lattice distortion. U substituted for Fe(III) in hematite maintained octahedral coordination in most cases. In general, comparison of the simulations with available experimental data provides further evidence for the structural incorporation of U in iron (hydr)oxide minerals.
authors.affiliation: Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States. sebastien.kerisit@pnl.gov
authors.forename: Sebastien
authors.initials: S
authors.lastname: Kerisit
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Felmy
authors.forename: Eugene S
authors.initials: ES
authors.lastname: Ilton
mesh_terms: D000327:Adsorption; D005290:Ferric Compounds / Q000737:chemistry*; D052203:Ferrosoferric Oxide / Q000737:chemistry; D058085:Iron Compounds / Q000737:chemistry; D007700:Kinetics; D008903:Minerals / Q000737:chemistry; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011848:Radioactive Pollutants / Q000737:chemistry*; D013499:Surface Properties; D014501:Uranium / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D058085:Iron Compounds; D008903:Minerals; D011848:Radioactive Pollutants; C094886:goethite; C000499:ferric oxide; C021024:ferric hydroxide; D014501:Uranium; D052203:Ferrosoferric Oxide